Filesets and global snapshots

A GPFS™ global snapshot preserves the contents of the entire file system, including all its filesets, even unlinked ones.

The state of filesets in the snapshot is unaffected by changes made to filesets in the active file system, such as unlink, link or delete. The saved file system can be accessed through the .snapshots directories and the namespace, including all linked filesets, appears as it did when the snapshot was created. Unlinked filesets are inaccessible in the snapshot, as they were in the active file system. However, restoring a snapshot also restores the unlinked filesets, which can then be re-linked and accessed.

If a fileset is included in a global snapshot, it can be deleted but it is not entirely removed from the file system. In this case, the fileset is emptied of all contents and given a status of 'deleted'. The contents of a fileset remain available in the snapshots that include the fileset (that is, through some path containing a .snapshots component) even after the fileset is deleted, since all the contents of the fileset are saved when a snapshot is created. The fileset remains in the deleted state until the last snapshot containing it is deleted, at which time the fileset is automatically deleted.

A fileset is included in a global snapshot if the snapshot is created after the fileset was created. Deleted filesets appear in the output of the mmlsfileset and mmlsfileset --deleted commands, and the -L option can be used to display the latest snapshot that includes a fileset.

During a restore from a global snapshot, attributes of filesets included in the snapshot can be altered. The filesets included in the global snapshot are restored to their former state, and newer filesets are deleted. Also, restore may undelete deleted filesets and change linked filesets to unlinked or vice versa. If the name of a fileset was changed since the snapshot was taken, the old fileset name will be restored.